The invention relates to an intake arrangement for combustion air of an internal combustion engine.
U.S. Pat. No. 5,526,777 discloses an intake arrangement for an internal combustion engine in a portable handheld work apparatus. An air filter is provided in a filter housing for purifying the combustion air. Unfiltered air is conveyed through an opening into the filter housing by the cooling blower of the engine and is moved along the air filter. The carburetor of the engine is connected to the clean air side of the filter housing and the engine draws dust-free combustion air into a combustion chamber of the engine via the air filter. When an intensely dirty ambient is present as is often the case for cutoff machines, the dust, which is contained in the air, deposits on the air filter and quickly clogs the same. For this reason, the power developed by the engine is affected. The large dust load of the air filter requires frequent cleaning so that a maintenance intensive operation of the engine results.
It is an object of the invention to provide an intake arrangement for the combustion air of an internal combustion engine with which a low maintenance continuous operation of the engine is provided with a minimized dust load of the air filter even with heavily dust-laden ambient air.
The intake arrangement for combustion air of the invention is for an internal combustion engine including an internal combustion engine of a portable handheld work apparatus. The engine includes a carburetor toward which combustion air laden with dust is drawn by the engine. The intake arrangement includes: an air filter assembly mounted upstream of the carburetor for purifying the combustion air of the dust; the air filter assembly including a filter housing and an air filter mounted in the filter housing for separating the dust from the combustion air; the air filter delimiting a contaminant space in the filter housing where the dust deposits and is separated from the combustion air; the filter housing having an opening formed therein through which the combustion air laden with dust passes into the contaminant space; and, carrier airflow means operatively connected to the contaminant space for conducting away the separated dust in a carrier airflow.
In the intake arrangement, means for conducting away the dust separated from the combustion air is provided on the side of the contaminant space and a carrier airflow is used for this purpose. The dust load of the air filter is reduced in this manner and a continuous discharge of dust separated at the air filter is ensured. The combustion air for the engine first flows into a contaminant space via an opening in the filter housing. The contaminant space is delimited by the filter housing and the filter. The combustion air is guided through the air filter with the dust or contaminants being separated and the combustion air then enters into a crankcase via an intake pipe section in the carburetor of the engine and into the combustion chamber of the engine. A discharge tube is connected to the contaminant space and connects the contaminant space of the filter housing to a flow channel. The carrier airflow is conducted in the flow channel. If dust drops from the air filter during operation of the work apparatus, then the contaminant reaches the discharge tube and is conducted away by the carrier airflow.
The flow channel is mounted approximately transversely to the discharge tube. In this way, a static pressure or underpressure is developed in the opening region of the discharge tube in the flow channel and this static pressure or underpressure supports the discharge of the filter cake or contaminant from the contaminant space and the discharge tube. It can be practical to permit the discharge tube to open into the flow channel at an acute angle. With this constructive measure, a suction action of the carrier airflow in the discharge tube is increased.
The geometric disposition of the flow direction of the combustion air in the filter housing relative to the discharge tube is so selected that the combustion air is so guided in the contaminant space of the filter housing that the combustion air runs at least transversely to the conveying direction of the contaminant or filter cake in the discharge tube. For this purpose, the longitudinal center axis of the opening for the entry of combustion air is arranged transversely to the discharge tube. In order to keep coarse contaminant particles from the contaminant space of the filter housing, it is practical to provide a plurality of openings in lieu of one opening to the entry of the combustion air. The diameter or cross-sectional area of the plurality of openings can then be selected smaller than that of a single opening.
The air filter is preferably formed as a flat structure having a rectangular, quadratic or circularly-shaped outline. The air filter spans a filter plane to which the longitudinal center axis of the discharge tube is aligned so as to be parallel or approximately perpendicular.
The discharge tube, which is arranged approximately perpendicular in the work position of the work apparatus (that is, directed to the earth center point), opens into the filter housing in a funnel-like manner expanding under the air filter. In this way, the contaminant or filter cake which drops off of the air filter can reach the discharge tube under the action of gravity.
The blower, which generates the carrier airflow is preferably a cooling air blower of the engine. The air filter is preferably configured as a planar or folded paper air filter.